Recent studies on cortical processing of sensory information highlight the importance of multisensory integration, and define precise rules governing reciprocal influences between inputs of different sensory modalities. We propose that psychophysical interactions between different types of sensory stimuli and linguistic synaesthesia share common origins and mechanisms. To test this hypothesis, we compare neurophysiological findings with corpus-based analyses relating to linguistic synaesthesia. Namely, we present Williams’ hypothesis and its recent developments about the hierarchy of synaesthetic pairings, and examine critical aspects of this theory concerning universality, directionality, sensory categories, and usage of corpora. These theoretical issues are verified against linguistic data derived from corpus-based analyses of Italian synaesthetic pairings related to auditory and tactile modalities. Our findings reveal a strong parallel between linguistic synaesthesia and neurophysiological interactions between different sensory stimuli, suggesting that linguistic synaesthesia is affected by tendencies similar to the rules underlying the perceptual association of distinct sensory modalities.